It is known that an organic polymer containing at least one reactive silicon group in the molecule is crosslinked by the formation of a siloxane bond, which is accompanied by hydrolysis and the like of the reactive silicon group due to moisture and the like even at room temperature, to obtain a rubber-like cured product.
Among the polymers having a reactive silicon group, a polymer having, as a main chain skeleton, a polyoxyalkylene-based polymer skeleton or a polyisobutylene-based polymer skeleton has been disclosed in Patent Document 1, Patent Document 2, and the like. Those polymers are already industrially produced and widely used for applications such as sealing material, adhesive, paint and the like.
By having a carbon-carbon bond as a main chain, the polyisobutylene-based polymer having a reactive silicon group is a material which remains strong against light or heat and also can exhibit endurance against long-term exposure. Similarly to Patent Document 3, for example, it has been shown that the polyisobutylene-based polymer is also usable for heat reflecting glass. On the other hand, by having an ether bond as a main chain, the polyoxyalkylene-based polymer having a reactive silicon group is susceptible to light or heat. Due to such reasons, the polyoxyalkylene-based polymer having a reactive silicon group is generally blended with an antioxidant, an ultraviolet absorbing agent, or a photostabilizer in combination. In particular, it has been already described in Patent Document 4 and thus well known that a hindered-amine-based photostabilizer with high molecular weight is effective for improving weather resistance. Furthermore, a technique of combining the polyoxyalkylene-based polymer having a reactive silicon group with a hindered-amine-based photostabilizer of >N—OR type (R is a long chain alkyl group) has been also described in Patent Document 5. Furthermore, a technique of combining the polyoxyalkylene-based polymer having a reactive silicon group with a triazine-based hindered-amine-based photostabilizer and a benzotriazole-based ultraviolet absorbing agent is also well known from Patent Document 6.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. S52-73998
Patent Document 2: Japanese Unexamined Patent Application, Publication No. S63-6041
Patent Document 3: Japanese Unexamined Patent Application, Publication No. H09-286895
Patent Document 4: Japanese Unexamined Patent Application, Publication No. S61-233043
Patent Document 5: Japanese Unexamined Patent Application, Publication No. 2015-89911
Patent Document 6: Japanese Unexamined Patent Application, Publication No. 2001-271057
The polyoxyalkylene-based polymer having a reactive silicon group is widely used as a sealing material for construction or a sealing material for industrial use. For those uses, weather resistance against sunlight over a long period of time is required, or stability against heat is required for industrial use. Due to such reasons, in a polyoxyalkylene-based polymer having a reactive silicon group, plural stabilizers are added in combination in general. In particular, the hindered-amine-based photostabilizer is suitable for enhancing the weather resistance of a polyoxyalkylene-based polymer having a reactive silicon group, and in particular, those with high molecular weight are considered to be effective as they are hardly washed out by water or the like. Furthermore, when a composition containing the polyoxyalkylene-based polymer having a reactive silicon group is colored, it is not so difficult to ensure the weather resistance due to the high shielding effect of calcium carbonate as white pigment, rutile type titanium oxide, or carbon black as black pigment, for example. On the other hand, with regard to a transparent composition, light can reach even the inside of a cured product so that it is difficult to maintain the weather resistance over a long period of time. In addition, there are some stabilizers that are colored red or yellow when used in combination with an amino group-containing silane coupling agent as an adhesiveness imparting agent. Under those circumstances, finding out a combination of additives that is not likely to cause discoloration of a cured product has remained not easy. Furthermore, for a sealing material, blending a large amount of calcium carbonate is generally carried out for imparting the reinforcing property or thixotropic property, or for lowering the cost. In addition, calcium carbonate is a filler with high whiteness. Due to such reasons, a sealing material containing calcium carbonate is not likely to have realization of the coloration that is caused by combined use of a stabilizer and an amine compound as described above, and thus there is almost no case in which the discoloration of a cured product is present.